The invention relates to a medical instrument for cutting tissue.
An instrument of this kind is known from U.S. Pat. No. 5,489,291.
Such instruments are used in minimally invasive surgery for detaching tissue in the human or animal body. To do so, a distal end of a shaft is guided to the operating site where the tissue that is to be detached is situated. To detach the tissue, a cutting element is moved in rotation by means of an external or internal motor. During the rotation, a blade formed on the cutting element cooperates in a cutting action with an edge of a window in the shaft, which edge is designed as a blade. The blade of the cutting element passes the blade of the window upon each revolution. To ensure that the tissue to be detached can be brought between the interacting blades, the shaft of such instruments is connected to a suction source. The suction effect of the suction source reaches through the inner hollow space of the shaft as far as the window, in order to suck the tissue to be detached through the window and into the shaft, such that the blades can sever the tissue. The detached tissue is sucked through the shaft by the partial vacuum.
The instrument known from U.S. Pat. No. 5,489,291 mentioned above comprises an outer shaft, which is beveled at its distal end. A tubular rotatable inner shaft, at whose distal end a cutting element is formed, is received in the outer shaft. The cutting element has several openings which, seen in a circumferential direction, are of the same width. Each of the openings has a blade.
The tissue to be detached is sucked into one of the openings of the cutting element rotating in the outer shaft. The tissue is then severed by means of the blade-type edge of the cutting element opening, into which the tissue to be detached is sucked, running past the leading rotating edge of the pointed part of the outer shaft. After the tissue has been detached, it is sucked through the inner shaft to the proximal end of the instrument.
Since the width of the several openings of the cutting element is the same, seen in a circumferential direction, it is found that only tissue whose width corresponds approximately to the width of the openings of the cutting element can be effectively and efficiently sucked into the openings and thus be detached. Tissue that is appreciably larger than the openings of the cutting element is either not sucked at all, or sucked only partially, into the openings of the cutting element. It has been found that, for a cutting element of a defined size, there is likewise a defined size of the tissue that can be effectively detached. Particularly for large tissue parts, multiple cuts are needed, which lead to fraying and leaves behind shreds of tissue.
Therefore, the disadvantage of the known instrument is that the tissue to be detached cannot in fact be detached very efficiently and satisfactorily.
It is therefore an object of the present invention to develop an instrument of the type mentioned at the outset in such a way that the cutting performance or cutting efficacy is improved.